The invention relates to a method for milling the flanks of a feed screw and to a feed screw milling machine.
Feed screws of the type under consideration are used in container filling machines such as, for example, bottle filling machines, in order to position a series of approaching containers at a specific distance corresponding to the respective incremental machine spacing. For this purpose, such feed screws are also arranged between successive stations of a filling machine, so that the containers are transferred at a predetermined distance from each other.
In order to transfer the containers, which generally either have no distance or only a small distance between themselves, to the feed screw, a spiral groove is milled into the feed screw, the pitch of the flanks of which varies along the length of the feed screw and, in this particular case, in such a manner that the pitch increases from the point where the containers enter the feed screw toward the point of exit.
The spiral shaped groove is milled into a feed screw blank by means of a milling tool that rotates at high rpm, with the feed screw blank rotating at a much lower rpm, while either the milling tool or the feed screw is moved at variable speed in the axial direction. If the feed screw which is to be produced is intended for use in the handling of rotationally symmetrical containers, the rotating milling tool is arranged relative to the feed screw blank in such a way that the shaft of the milling tool extends at a right angle with respect to the longitudinal axis of the feed screw blank. The milling tool has a linear milling edge and mills the spiral shaped grooved independent of the instantaneous feed screw pitch with the required precision and without flank errors, so that the production of a feed screw for rotationally symmetrical containers is largely free of problems.
However, if the feed screw is intended for use in handling containers that are not rotationally symmetrical, it should then have a spiral shaped groove with a cross sectional area that is suited to the container which is to be handled. In order to mill the spiral shaped groove in this case, the arrangement is configured such that the shaft of the milling tool extends parallel to the longitudinal axis of the feed screw blank.
If the milling tool has a shape that precisely agrees with the associated cross sectional area of the container shape that is to be handled, then, as a result of a changing pitch when the groove is milled, there is an increasingly greater feed screw flank error as the pitch increases, that is, the spiral shaped groove becomes narrower as the pitch becomes increasingly larger, whereby the crooked positioning or even a crushing of the containers can occur. This feed screw flank error presently is corrected by employing a specifically oversized milling tool, but has the disadvantage that the spiral shaped groove that is milled-in only agrees with the shape of the container which is to be handled at a very specific pitch. But at any of the other areas along the feed screw the containers are not grasped and transferred in an error free manner, since the pitch usually increases in the direction from the start of the feed screw toward the end.
A further feature of the invention is the development of a method for milling the flanks of a feed screw of the type considered, such that the occurrence of an error at the feed screw flank with variable feed screw pitch is avoided to the greatest degree possible Additionally, a feed screw milling machine should be specified whereby a groove specifically defined for the associated cross section of a container shape which is to be handled can be milled into a feed screw blank without the appearance of an error in the flank of the feed screw at variable pitches.